From: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Loading unauthenticated FDT blobs directly from storage is a security hazard,
so this should only be allowed when running with UEFI Secure Boot disabled.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Signed-off-by: Leif Lindholm <leif.lindholm@xxxxxxxxxx>
---
drivers/firmware/efi/arm-stub.c | 39 +++++++++++++++++++++++++++++++++++----
1 file changed, 35 insertions(+), 4 deletions(-)
diff --git a/drivers/firmware/efi/arm-stub.c b/drivers/firmware/efi/arm-stub.c
index 19239a9..41114ce 100644
--- a/drivers/firmware/efi/arm-stub.c
+++ b/drivers/firmware/efi/arm-stub.c
@@ -12,6 +12,30 @@
*
*/
+static int __init efi_secureboot_enabled(efi_system_table_t *sys_table_arg)
+{
+ static efi_guid_t const var_guid __initconst = EFI_GLOBAL_VARIABLE_GUID;
+ static efi_char16_t const var_name[] __initconst = {
+ 'S', 'e', 'c', 'u', 'r', 'e', 'B', 'o', 'o', 't', 0 };
+
+ efi_get_variable_t *f_getvar = sys_table_arg->runtime->get_variable;
+ unsigned long size = sizeof(u8);
+ efi_status_t status;
+ u8 val;
+
+ status = f_getvar((efi_char16_t *)var_name, (efi_guid_t *)&var_guid,
+ NULL, &size, &val);
+
+ switch (status) {
+ case EFI_SUCCESS:
+ return val;
+ case EFI_NOT_FOUND:
+ return 0;
+ default:
+ return 1;
+ }
+}
+
static efi_status_t efi_open_volume(efi_system_table_t *sys_table_arg,
void *__image, void **__fh)
{
@@ -144,7 +168,7 @@ unsigned long __init efi_entry(void *handle, efi_system_table_t *sys_table,
/* addr/point and size pairs for memory management*/
unsigned long initrd_addr;
u64 initrd_size = 0;
- unsigned long fdt_addr; /* Original DTB */
+ unsigned long fdt_addr = 0; /* Original DTB */
u64 fdt_size = 0; /* We don't get size from configuration table */
char *cmdline_ptr = NULL;
int cmdline_size = 0;
@@ -196,9 +220,13 @@ unsigned long __init efi_entry(void *handle, efi_system_table_t *sys_table,
goto fail_free_image;
}
- /* Load a device tree from the configuration table, if present. */
- fdt_addr = (uintptr_t)get_fdt(sys_table);
- if (!fdt_addr) {
+ /*
+ * Unauthenticated device tree data is a security hazard, so
+ * ignore 'dtb=' unless UEFI Secure Boot is disabled.
+ */
+ if (efi_secureboot_enabled(sys_table)) {
+ pr_efi(sys_table, "UEFI Secure Boot is enabled.\n");
+ } else {
status = handle_cmdline_files(sys_table, image, cmdline_ptr,
"dtb=",
~0UL, (unsigned long *)&fdt_addr,
@@ -209,6 +237,9 @@ unsigned long __init efi_entry(void *handle, efi_system_table_t *sys_table,
goto fail_free_cmdline;
}
}
+ if (!fdt_addr)
+ /* Look for a device tree configuration table entry. */
+ fdt_addr = (uintptr_t)get_fdt(sys_table);
status = handle_cmdline_files(sys_table, image, cmdline_ptr,
"initrd=", dram_base + SZ_512M,
--
1.7.10.4
--
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